Process of sweetening sour petroleum hydrocarbons



United States Patent 3,12%,244 PRUQESS 6F SWEE'IENENG DUR PETROLEUM HYDRGQARBUNS Thomas J. Wallace, Elizabeth, NJ, assignor to Esso Research and Engineering ilompany, a corporation of Delaware No Drawing. Filed Apr. 28, 1%1, Ser. No. 107,004 13 Claims. (fill. 208-404) This invention relates to a process of sweetening sour petroleum hydrocarbons comprising contacting said hydrocarbons with an organic polyketo oxidation catalyst. More particularly, this process relates to sweetening sour petroleum distillates. Specifically this invention relates to a process of sweetening sour petroleum distillates containing mercaptans and mercaptide compounds comprising contacting the distillates with a saturated alkyl polyketo organic oxidation catalyst which catalyst enhances the conversion of mercaptans and mercaptides to disulfides. The term keto as herein used is understood to stand for the group.

In the manufacture of light hydrocarbon oils and motor fuels by modern cracking methods, substantial amounts of mercaptans are formed when sulfur containing heavy oils are used for cracking-stocks. In fractionating the cracked products, the mercaptans become concentrated in the light fractions normally used for gasoline and fuel oils. The mercaptans impart'a highly objectionable odor to the fraction, decrease the octane number, and must be removed or converted to less objectionable substances before it is suitable for blending into a marketable product.

The oxidation catalysts of this invention are sufiiciently active to sweeten sour distillates having a comparatively high mercaptan content; however, it is preferred to remove a major portion of the mercaptans from the distillate prior to final sweetening. For gasoline to which alkyl lead compounds are not to be added, the presence of the disulfides is not particularly objectionable. On the other hand, the presence of disulfides in gasoline to which alkyl lead compounds are to be added is objectionable because the presence of the disulfides reduces the sensitivity of the gasoline to the addition of the lead to even a greater extent than a corresponding concentration of mercaptans. Since most gasolines'now marketed are treated with tetraethyl lead or tetramethyl lead, it follows that it is desirable to remove most-of'the mercaptans rather than to merely convert them to disulfides. This, of course, is as critical with fuel oils. Conventional treating methods can remove from about 50 to 95% of the mercaptans, but still leave sufiicient mercaptans to produce a product which is-sour. An example of such a mercaptan removal process is the use of caustic soda solution with or without a so-called solutizer. Naphthas treated by such processes generally require a finishing treatment with the wellknown doctor process or other equivalent process in order to obtain a satisfactory sweet product. I have now unexpectedly found a class of organic polyketo oxidation catalyst which efiectively and efiiciently enhances the conversion of the mercaptans present in the petroleum distillate to less objectionable disulfides and results in'obtaining a product which gives a negative doctor test and which is accordingly doctor sweet.

The hydrocarbon mixture containing mercaptan compounds is said to be sour or positive to the doctor test if it contains more than about .004% sulfur, calculated as mercaptans. This relates to a mercaptan number "Ice (RSH No.) of 0.4. It is said to be sweet or to be negative to the doctor test when the sulfur concentration is below that value. The mercaptan number is defined as the milligrams of mercaptan sulfur per milliliters of oil, and is generally determined by titration with standard copper salt solution. The doctor test is more fully described in US. Patent 2,543,953, dated March 6, 1951.

It is the object of the present invention to provide an efiicient and economic method for sweetening sour hydrocarbon mixtures. It is another object of this invention to provide a finishing treatment whereby-petroleum distillates which have been treated by conventional sweetening processes but which still contain small but objectionable amounts of mercaptans may be made sweet in order to have a more marketable product. A further object is to carry out the sweetening by contacting the sour distillates with the novel oxidation catalysts of this invention. A still further object of this invention is to produce a hydrocarbon mixture substantially reduced in mercaptans without pretreating said mixtures.

In one embodiment of my invention a sour petroleum distillate is sweetened by contacting the distillate with the organic oxidation catalyst of this invention to produce a distillate which is either negative to the doctor test or substantially reduced in mercaptan number.

In a further embodiment of my invention a sour petroleum distillate containing mercaptan compounds is first treated'in a conventional manner with aqueous caustic solution to remove 50-95% of the mercaptans present leaving sufficient mercaptans in the distillate to give a mercaptan number of between 0.40 and about 15 or better, preferably between 0.4 and 6.00, which gives a positive doctor test. To the sour distillate is added a suflicient amount of a saturated lower alkyl diketo hydrocarbon soluble organic oxidation catalyst of this invention in the presence of a trace of caustic, and oxygen for a suflicient period of time to reduce the mercaptans to a value which give a negative doctor test resulting in a sweetened'distillate. The catalyst is soluble in the oil layer and the oxidation of the mercaptans to disulfides takes place at the interphase and in the oil layer. The oxidation reaction may be carried out in either a continuousor batch process.

Sweetening of the sour hydrocarbon distillate is affected by oxidation of the mercaptans to disulfides. Accordingly, an oxidizing agent is present in the reaction mixture. Air is preferred, although oxygen or other oxygencontaining gases may be utilized. Depending upon the content of mercaptans in the distillate, there may already be suflicient entrained or dissolved oxygen or air in the distillate to accomplish the desired sweetening. How ever, when distillate containing higher concentrations of mercaptans are sweetened, itis generally necessary to introduce some air into the reaction. This may be done by bubbling air into the reactor or contacting vessel.

In a continuous process wherein the caustic wash pretreatment is carried out concurrently with the oxidation catalyst sweetening, the aqueous caustic Wash solution is passed down in a vessel, countercurrently to an ascending stream of sour petroleum distillate. The oxidation catalyst of this invention may be added to the sour petroleum distillate prior to being contacted with the caustic wash solution or to the partially sweetened distillate immediately after countercurrent contact with the caustic solution. Where additional air is required it may be bubbled into the vessel in which the caustic treatment takes place or it may be added to the partially sweetened petroleum distillate after it has been caustic treated or when enroute to storage.

In a batch process the oxidation catalyst, aqueous caustic solution, sour distillate, and air may be mixed in the reaction zone; the mixture allowed to settle and the sweetened gasoline containing the catalyst removed from the upper portion of the reaction zone and taken to storage. The aqueous caustic solution is removed from the lower portion of the reaction vessel and taken to conventional apparatus for regenerating spent caustic. The sweetened petroleum distillate can be washed with water to remove any entrained caustic.

Reaction temperature is not particularly critical but it should not be so high that vaporization, cracking, or undesirable side reactions take place. Usually, the sweetening reaction is carried out at ambient temperature. Pressure is also not particularly critical and the reaction is normally carried out at atmospheric pressure. However, where high temperatures are used high pressures can be utilized in order to keep the reactants in the liquid phase. The reactants are contacted with the catalyst for suflicient time so that the distillate being treated is substantially reduced in mercaptans present and a sweet distillate results. This can take from a few minutes up to ten days or more.

Due to the high activity of my organic catalysts, very small amounts of catalysts may be eifectively used to obtain doctor sweet hydrocarbon products. Since the oxidation catalysts are soluble in the hydrocarbon layer, the sweetened product contains the catalysts. It has been unexpectedly found that not only do the catalysts enhance the conversion of mercaptans to disulfides but they apparently also inhibit the formation of gum in the sweetened petroleum distillate product to some extent.

Petroleum distillates containing mercaptan and mercaptide compounds can be sweetened in accordance with this process. Various petroleum distillates, such as virgin and cracked naphthas, kerosene, gas oil, heating oil fuel oil, gasoline and the like may be sweetened in accordance with my process. Preferable naphthas boiling within the range of 100 F. to 750 F. are sweetened. Crude and residual oils may also be sweetened. Oxida tion of the mercaptans to disulfides is carried out by contacting them with my novel catalyst in the presence of base and oxygen or air.

Where the sour hydrocarbon mixture to be sweetened is very viscous, a lighter petroleum distillate or organic solvent may be added to improve the viscosity of the material to be treated. Examples are methyl cyclohexane, xylene, benzene, pentane, hexane, heptane, light cat. naphtha, etc.

The oil soluble organic saturated alkyl polyketo oxidation catalysts that can be used in accordance with my invention are encompassed by the following formula:

The alkyl constituents of the above formula may be further substituted by the following groups: Nl-l Cl, Br, F, I, OH, Cl, etc.

It can readily be seen from the above formula that my oxidation catalysts contain a basic functional group comprising at least two keto groups attached to a saturated alkyl containing 1 to 3 carbon atoms, namely,

2lu(fi The catalyst may contain two or more of these functional keto groups. The keto groups may be part of a ketone compound or, on the other hand, a carboxylic acid ester compound. A catalyst compound may be a diketone, dicarboxylic ester, or a ketoacid ester compound. The alkyl substituent separating the two keto groups can contain 1 to 3 carbon atoms which is critical. The alkyl ester group of an acid ester compound may contain 1 to 6 carbon atoms. Examples of compounds coming within the scope of this invention are diethyl malonate, diethyl succinate, ethyl acetoacetate, 2,4-pentanedione, tricarboethoxymethane, 1,1,2tricarboethoxyethane, 2,4,6- triketoheptane, and tetraacetylethane. Sufficient oxidation catalyst is added to enhance the conversion of at least a portion of the mercaptans to disulfides. The amount of catalyst added in any particular situation will depend upon the amount of sweetening desired, the amount of time allowed for sweetening a particular sour distillate, the amount of mercaptans present in the distillate, the number of functional keto groups, i.e.,

present in the catalyst and the temperature at which sweetening is carried out. The concentration of catalyst that is used can be 0.0001 to 1.0 weight percent based upon the hydrocarbon being treated. Though concentrations of 0.01 to 0.6 weight percent are preferred in most instances, concentrations of catalysts of 0.002 to 0.100 can also effectively be used. Generally, the upper limit of the amount of catalyst which is used is determined by economic considerations and the amount of foreign matter than can be tolerated in the end product. The reaction is carried out in the liquid phase.

The sweetening reaction is carried out in the presence of a basic reagent. The basic reagent may be sodium, potassium, ammonium hydroxides or highly basic amino compounds such as pyridine, etc. The concentration of caustic used in the sweetening process will depend upon the amount of mercaptans present which will depend upon whether or not the sour petroleum distillate has been previously treated to remove from 5-95% of the mercaptans originally present in the distillate. Where the sour distillate was treated in the conventional caustic wash process, the amount of caustic entrained in the distillate from the pretreatment is usually sufiicient to carry out the sweetening step. Where it is desired to reduce the mercaptan content of the petroleum distillate but it is not necessary to have a doctor sweet product, the conventional caustic pretreat may be omitted. However, under such circumstances, it is generally necessary to have a higher concentration of potassium or sodium hydroxide present during the sweetening process.

In carrying out the invention, sufiicient oxygen is added to the sour petroleum distillate being treated to react with the mercaptans present. The necessary oxygen may be added by contacting the distillate with pure oxygen, air, or other free oxygen containing gases. The oxygen may be added before adding the catalyst but preferably is added after contacting the distillate with the catalyst. The sour distillate containing the oxygen and catalyst in solution is then allowed to stand for a sufficient time to permit the conversion of the mercaptans by oxidation to disulfides. The conversion may take place during the caustic wash treatment in the contacting zone, enroute to storage, or in storage tanks. Frequently, there is sufii cient oxygen already entrained in the oil to carry out the sweetening process. Where oils containing high concentrations of mercaptans are to be treated, it may be necessary in order to obtain a sufiicient concentration of dissolved oxygen in the distillate to inject air into the oil or to permit the oil to stand in storage in contact with air. This will normally provide an excess of the quantity of the dissolved oxygen required to complete the oxidation of substantially all the mercaptans present.

Depending upon the temperature, the amount of catalyst present, the concentration of oxygen dissolved in the oil, the mercaptan content of the oil, and the degree of sweetening desired, the time necessary for carrying out the sweetening reaction may vary from a few minutes to six days or more. Generally, the time required for the sweetening step is between about 15 minutes and 24 hours. Preferably in most sweetening operations a doctor sweet product can be obtained in about 1 to 6 hours. However, when there is a substantial amount of mercaptans present, for example distillates having a mercaptan number of from about 14 up to 20 or more, it may be necessary in order to substantially reduce the mercaptan number of the distillate being treated, to have the sweetening reaction carried out for 24 hours or more. The sweetening reaction proceeds very well at atmospheric pressure and ambient temperature and generally will be carried out under these conditions. The time required for a given degree of sweetening, however, may be reducedv 4070% by increasing the temperature of the treated hydrocarbons up to about 130 C. The reaction, however, may be readily carried out at temperatures between 100 C. with temperatures of 2040 C. being preferred. The pressure at which the reaction is carried out is not critical and is generally atmospheric pressure. Sub-atmospheric and super-atmospheric pressures can be used and the higher pressures are used when elevated temperatures are used in order to maintain the reaction in the liquid phase.

Various types of reactors or contacting zones may be used to carry out the process of this invention and which is used will depend on whether the reaction is carried out in a batch or a continuous process. In one embodiment of the invention wherein the sour distillate is sweet ened concurrently with the caustic wash treatment, a sour distillate and caustic treat solution are countercurrently contacted in a vertical, cylindrical vessel. The aqueous caustic solution is introduced at the top of the vessel and passes downward countercurrently into an ascending stream of sour hydrocarbon. The oxygen and the catalyst can be introduced, singularly or together, with the sour feed, in the contacting vessel, or with the withdrawn partially sweetened distillate. The catalysts of this invention are hydrocarbon soluble and remain with the hydrocarbon being treated. The sweetened hydrocarbon and catalyst are removed from the top of the vessel and the aqueous caustic solution is removed from the bottom of the vessel. In a batch process, a conventional stirred reactor may be used.

In a preferred embodiment of my invention, 10,000 b./d. of sour light cat. naphtha boiling in the range of about 140 to 410 F. and having a mercaptan number of about 20 to 25 is introduced into the bottom of a treating vessel and continuously ascends countercurrently to a descending stream of 15 B. concentration of aqueous sodium hydroxide solution at a rate of 1 to 2% by volume of caustic solution to volume of sour light cat. naphtha per hour. The caustic solution may or may not contain a solutizer. Caustic wash treatment reduces the mercaptan number of the naphtha to about 5 by partial solvent extraction of the mercaptans present. There are, however, sufficient mercaptans remaining in the naphtha to give a positive doctor test. To the partially sweetened naphtha and in accordance with this invention, 0.002 to 0.10 weight percent, based on naphtha being treated, of a compound of the following structure is added:

The R substituents may be the same or different, and will be oxidation catalysts which are diketones, keto acid esters or diesters. As previously stated the oxidation catalyst may be added to the sour naphtha prior to, simultaneous with the caustic wash or after the caustic wash treatment. The sweetening process is generally carried out at ambient temperatures and atmospheric pressure. Air is bubbled into the contact vessel or added to the parially sweetened naphtha as needed in order to obtain substantially complete conversion of the mercaptans present to disulfides. The treated naphtha is then taken to storage. It is found that after between about 15 minutes and about 24 hours that the mercaptan number has been reduced to 0.30 and the naphtha is negative to the doctor test and accordingly sweet. Prior to sending the sweetened gasoline to storage, it may be subjected to a water wash to remove any entrained caustic solution.

The invention is further exemplified by various runs reported in the following examples:

EXAMPLE 1 A light cat. naphtha derived from Middle East crude oil with a boiling range of 50 to 450 F. and having a mercaptan number of 3.00 was divided into four portions of 300 ccs. each. To each 300 cc. sample of naphthav was added milligrams of sweetening reagent. There was sufficient air entrained in the naphtha. to carry out the oxidation of the mercaptans to disulfides. About 0.3 ccs. of 20% sodium hydroxide were used in each run. The amount that the mercaptan number was reduced for each reagent used is tabulated below in Table I:

Table I Reagent RSH# Time,

0.68 6 0.00 6 Ethyl Acetoaoetate 0. 04 6 Ethyl Suceinate 0.02 6

The last three reagents produced a doctor sweet sample within 6 hours. The N,N'-disecondary butyl p-phenylene diamine which is a known commercial sweetening agent, produced a samplewhich was still sour after 6 hours.

EXAMPLE 2 In order to show the efficiency of my sweetening agents, another sample of light cat. naphtha boiling in the range of to 330 F. was divided into four equal portions of 300 ccs. each. The naphtha had a mercaptan number of 14.3.

To each of the four samples were added 80 milligrams of the agents listed below in Table II. About 0.3 ccs. of 20% sodium hydroxide were added to each of the runs. There was suflicient dissolved air present to carry out the reaction. The reactants were mixed together in order to obtain efticient contact between the reagents and the naphtha to be sweetened and then allowed to settle. The mercaptan number of the naphtha was checked after 24 hours with the below tabulated results:

Though none of the reagents produced doctor sweet products after 24 hours, they did substantially reduce the mercaptan number of the samples. All of the sweetening agents of this invention were at least 6 times more efiective than the presently used phenylene diamine compound.

The above examples were introduced to illustrate the novelty and utility of the present invention but not with the intention of unduly limiting the same.

What is claimed is:

1. A process for treating a sour gasoline fraction con taining mercaptans which comprises contacting said fraction in the presence of an aqueous caustic solution and air with diethyl malonate at about ambient temperature and pressure for from a few minutes to about 24 hours.

2. A process for treating a sour gasoline fraction containing mercaptans which comprises contacting said fraction in the presence of an aqueous caustic solution and air with diethyl succinate at about ambient temperature and pressure for from a few minutes to about 24 hours;

3. A process for treating a sour gasoline fraction conas u an oxidizing agent with an aqueous caustic solution and an organic oxidation catalyst having the following formula:

taining mecaptans which comprises contacting said fraction in the presence of an aqueous caustic solution and air with ethyl acetoacetate at about ambient temperature and pressure for from a few minutes to about 24 hours.

4. A process for treating a sour gasoline fraction containing mercaptans which comprises contacting said fraction in the presence of an aqueous caustic solution and air with 2,4-pentane dione, at about ambient temperature and pressure for from about a few minutes to about 24 hours.

5. The process of sweetening a sour hydrocarbon fraction containing mercaptan compounds which comprises contacting said hydrocarbon fraction in the presence of an oxidizing agent with an aqueous basic solution and an organic oxidation catalyst having the following formula:

wherein R is selected from the group consisting of s)n a for a sufficient period of time to reduce the mercaptan concentration and separating a hydrocarbon fraction of substantially reduced mercaptan concentration.

6. The process of sweetening a sour hydrocarbon fraction containing mercaptan compounds which comprises contacting said hydracarbon fraction in the presence of an oxidizing agent with an aqueous caustic solution and a hydrocarbon soluble organic oxidation catalysthaving the following formula:

wherein R is selected from the group consisting of n ttin -ens and for a sufficient period of time to reduce the mercaptan concentration and separating a hydrocarbon fraction of substantially reduced mercaptan concentration.

7. The process of sweetening a sour hydrocarbon fraction containing mercaptan compounds which comprises contacting said hydrocarbon fraction in the presence of II II o o for a sufiicient period of time to reduce the mercaptan concentration and separating a hydrocarbon fraction of substantially reduced mercaptan concentration.

9. The process of sweetening a sour hydrocarbon fraction containing mercaptan compounds which comprises contacting said hydrocarbon fraction in the presence of an oxidizing agent with an aqueous caustic solution and an organic oxidation catalyst having the following formula:

for a sufficient period of time to reduce the mercaptan concentration and separating a hydrocarbon fraction of substantially reduced mercaptan concentration.

10. The process of sweetening a sour hydrocarbon fraction containing mercaptan compounds which comprises contacting said hydrocarbon fraction in the presence of an oxidizing agent with an aqueous caustic solution and diethyl malonate for a sufiicient period of time to reduce the mercaptan concentration and separating a hydrocarbon fraction of substantially reduced mercaptan concentration.

11. The process of sweetening a sour hydrocarbon fraction containing mercaptan compounds which comprises contacting said hydrocarbon fraction in the presence of an oxidizing agent with an aqueous caustic solution and diethyl succinate for a suflicient period of time to reduce the mercaptan concentration and separating a hydrocarbon fraction of substantially reduced mercaptan concentration.

12. The process of sweetening a sour hydrocarbon fraction containing mercaptan compounds which comprises contacting said hydrocarbon fraction in the presence of an oxidizing agent with an aqueous caustic solution and ethyl acetoacetate for a sufficient period of time to reduce themercaptan concentration and separating a hydrocarbon fraction of substantially reduced mercaptan concentration.

13. The process of sweetening a sour hydrocarbon fraction containing mercaptan compounds which comprises contacting said hydrocarbon fraction in the presence of an oxidizing agent with an aqueous caustic solution and 2,4-pentane dione for a sufiicient period of time to reduce the mercaptan concentration and separating a hydrocarbon fraction of substantially reduced mercaptan concentration.

References (Iited in the file of this patent UNITED STATES PATENTS 2,197,477 Lyons et al Apr. 16, 1940 2,616,832 Browder et al. Nov. 4, 1952 2,773,861 Musselman Dec. 11, 1956 3,013,965 Ferrara et al Dec. 19, 1961 s PATENT OFFICE CORRECTION f April 7 1964 UNITED STATE CERTIFICATE OF Patent No. 3,128344 Thomas J Wallace e above numbered patppears in th hould read as It is hereby certified that error a ent requiring correction and that the said Letters Patent s corrected below.

hown

line 41, the formula should appear as 5 Column 7,

n the patent:

below instead of as i 1-3 column 7, lines 46 and 67, the formula, each occurrence should appear as shown below instead of as in the patent:

-o-(ca -ca I 2 n 3 z i Signed and sealed this 15th day of September 1964.

(SEAL) Attest:

EDWARD J o BRENNER ERNEST W SWIDER Commissioner of Patents 1 Attesting Officer 5 i 

5. THE PROCESS OF SWEETENING A SOUR HYDROCARBON FRACTION CONTAINING MERCAPTAN COMPOUNDS WHICH COMPRISES CONTACTING SAID HYDROCARBON FRACTION IN THE PRESENCE OF AN OXIDIZING AGENT WITH AN AQUEOUS BASIC SOLUTION AND AN ORGANIC OXIDATION CATALYST HAVING THE FOLLOWING FORMULA: 